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Simulated Production and Biological Efficiency of Sheep Flocks in a Shifting Environment¹

Texas Agricultural Experiment Station, College Station 77843

Abstract

Nine genetic combinations with potential mature ewe sizes (WMA) of 30, 35 and 45 kg and potential mature peak day milk production levels (GMLKL) of .90, 1.30 and 1.75 kg were simulated continuously during an average base year (BY), a drought year (DY), and two recovery years (RY1 and RY2) in a northern Kenya production system. Nomadic herders constantly monitor animal activity and utilize the milk and meat produced. Input parameters for the Texas A&M sheep simulation model were set to characterize the response of sheep to conditions found in this production situation in an attempt to examine recovery from the DY and to distinguish among genotypes. Generally, larger WMA had greater average recovery percentage (100 RY2/BY) for total live weight sold per ewe (79.0, 90.0 and 98.6% for WMA of 30, 35 and 45 kg, respectively). Two genotypes (WMA/GMLKL) having the lowest recovery percentages were 30/1.75 (72%) and 35/1.75 (73%). Recovery for average annual milk production per ewe was more uniform across WMA, with average recoveries of 80.4, 87.3 and 87.5% for WMA of 30, 35 and 45, respectively. Output:input ratios were used to measure flock performance for meat, milk, energy and protein production because the only input of concern was forage (or land area). The 45/1.75 flock consistently ranked highest when compared with other genotypes. The 35/1.30, representing the current breed, also ranked highly. Compared with the current breed's output, these simulated results indicate that the environment could support a larger, higher milking genotype that would increase the offtake of the flock, and that the 30 WMA genotypes would not be as productive in this environment. The 30/1.75 and 35/1.75 flocks experienced markedly depressed performance due to the drought, suggesting that increasing only milk production would not be advantageous.

¹ Actual data were collected by Dr. C. R. Field of the Integrated Project in Arid Lands, part of UNESCO's Man and the Biosphere Program. Model development and analysis were supported in part by funds from the United States Agency for International Development, Title XII, Small Ruminants Collaborative Research Support Program under grant No. AID/DSAN/XII-G-0049 in collaboration with the Kenya Ministry of Agriculture and Livestock Development.

² Anim. Sci. Dept.